Method of making a flexible member having increased service life

ABSTRACT

A method of making a flexible member having increased service life with the member being of the type designed for use in a fluid pressure system in which a predetermined flex wrinkle pattern or a modification thereof is imparted to a surface of the flexible member to improve the flexing properties while the member is operating in such system. This pattern may consist of a simulation of the actual flex wrinkle pattern of a previously operating flexible member or be a compromise which employs a plurality of grooves having substantially the same pitch as the wrinkles. This invention results in the increased flex life and improved low temperature performance of the flexible member.

United States Patent Burkley [4 Sept. 12, 1972 [54] METHOD OF MAKING AFLEXIBLE 2,288,840 7/1942 Raiche ..l8/47 R X MEMBER HAVING INCREASED2,958,148 11/1960 Sylvester et a1 ..264/220 X 3,313,873 4/1967 Dembiak..264/219 X SERVICE LIFE 3,473,989 10/1969 Richmond ..264/227 XInventor: Thomas E. Burkley, Akron, Ohio The Goodyear Tire 8: RubberCompany, Akron, Ohio Filed: March 23, 1970 Appl. No.: 24,931

Related U.S. Application Data Division of Ser. No. 679,731, Nov. 1,1967, Pat. No. 3,598,155.

Assignee:

References Cited Primary Examiner-Robert F. White AssistantExaminer-Allen M. Sokal Attorney-F. W. Brunnerand Robert H. l-latton [57] ABSTRACT A method of making a flexible member having increasedservice life with the member being of the type designed for use in afluid pressure system in which a predetermined flex wrinkle pattern or amodification thereof is imparted to a surface of the flexible member toimprove the flexing properties while the member is operating in suchsystem. This pattern may consist of a simulation of the actual flexwrinkle pattern of a previously operating flexible member or be acompromise which employs a plurality of grooves having substantially thesame pitch as the wrinkles. This invention results in the increased flexlife and improved low temperature performance of the flexible member.

12 Claims, 8 Drawing Figures "PATENTEDszmasn 3 691 68 smzu 1 er 2 FIG. 2

FIG. 3

4 INVENTOR.

THOMAS E BURKLEY ATTORNEY PATENTEBsEP 12 1812 3.651. 268

sum 2 or 2 INVENTOR. THOMAS E. BURKLEY ATTORNEY METHOD OF MAKING AFLEXIBLE MEMBER HAVINGINCREASED SERVICE LIFE This is a divisionalapplication of my Co-pending application Ser. No. 679,731 filed Nov. 1,I967 now issued as U.S. Pat. No. 3,598,155.

BACKGROUND OF THE INVENTION This invention relates to a method ofproducing an improved flexible member of the type designed for use in afluid pressure system. More specifically, this invention relates to amethod of increasing the service life of a flexible member of the typeused, for example, in a pneumatic suspension or brake control systemreferred to generally as the rolling lobe air spring and rolling sleevediaphragm respectively.

Rolling lobe air springs are normally employed for shock absorbing, loadsupporting and vibration isolation in vehicle suspension systems andother industrial and military applications. The typical pneumaticpressure system of this type operates as follows. A tubular essentiallycylindrical flexible member of fabric reinforced elastomeric materialsuch as rubber or the like is positioned between retaining elements.This flexible member has clamping means at the peripheral edge portionsthereof in order to attach the member to the retaining elements and forman airtight chamber capable of supporting a load of varying proportions.A piston, acting upon the flexible member, creates a rolling motion inthe sidewall of the flexible member consequently causing the compressionand expansion of the column of air confined in the chamber. An excellentdetailed description of the construction, operation, and production ofthe rolling lobe type air spring is contained in Hirtreiter US. Pat. No.3,043,582.

Similarly, rolling or sleeve diaphragms of the type used in pneumaticbrake control systems employ a cup or hat-shaped flexible fabricreinforced member of elastomeric material with a cylindrical orfrusto-conical sidewall which may have a closed base or may be open onboth ends. The peripheral edge portion or lip of the diaphragm typicallyis attached to the central wall portion of a brake chamber. The closedend portion or the other peripheral edge portion of the open endattached to the piston thus forms an airtight compartment. In someinstances, when air under pressure is admitted into this compartment,the diaphragm is deflected thereby creating a rolling motion in thesidewall of the diaphragm to move a plunger contained within the brakechamber.

Those skilled in the art are aware that one of the major problemsencountered in such systems is the premature failure of the flexiblemember due to flex cracking in the area which is subjected to themaximum flexing during operation in such systems. This cracking may alsooccur prematurely when the flexible member is exposed to extremely lowtemperatures in frigid areas as the result of the consequently stiffenedcondition of the elastomeric material after such exposure.

The present invention discloses flexible diaphragms or members of animproved construction which prolongs substantially the flex lift evenunder severe low temperature conditions as well as a method of producingsuch a flexible member. It has been found that forming, prior toinstallation in a fluid pressure system, the flex wrinkle pattern on thesurface of the flexible member at least in the area subjected to themaximum flexing, will control the flex characteristics and alleviatemany of the normal deteriorating stresses when the flexible member isoperating in the system. In other words, the actual flex wrinkle patternis effectively simulated on the compression surface of the flexiblemember with the wrinkles therein acting as hinge points which facilitatethe flexing in the area of the member most susceptible to failure orcracks due to flexing or low temperatures.

This is accomplished by reproducing on the compression surface of theflexible member, the actual flex wrinkle pattern, created on thecompression surface of a flexible member by the operation of a similardiaphragm in a fluid pressure system for a period of time sufficient tocreate the flex wrinkle. This may be accomplished in a number of ways,some of which will be hereinafter described.

OBJECTS OF THE INVENTION The primary object of this invention is toprovide a method which will control the flex characteristics andalleviate the stresses created in a flexible member to provide asubstantial improvement in the general durability thereof without anappreciable increase in manufacturing costs.

Another important object of this invention is to significantly prolongthe flex life of a flexible elastomeric member of the type used in afluid pressure system such as an air spring suspension or pneumaticbrake control system.

Still another object of this invention is to provide an improvedflexible elastomeric member such as a rolling lobe air spring androlling sleeve air brake diaphragm which will resist wall cracking whenthe product is operating during extreme cold weather exposures.

A further object of this invention is to facilitate the operation of aflexible member of the type designed for use in a fluid pressure systemby providing an improved contour to reduce resistance to the rollingmotion of such member particularly at low pressures.

Other objects and advantages of this invention will become apparenthereinafter as the description thereof proceeds, the novel features,arrangements and combinations being clearly pointed out in thespecification as well as the claims thereunto appended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of onetype of flexible member illustrating this invention;

FIG. 2 is a section taken substantially through 2-2 of FIG. 1;

FIG. 3 is a modification of the invention shown in FIG. 2;

FIG. 4 is an elevation showing one method of producing the inventionshown in FIG. 3;

FIG. 5 is a modification of the invention shown in FIG. 3;

FIG. 6 is another modification of the invention shown in FIG. 3;

FIG. 7 is a perspective view of another type of flexible member forwhich this invention is useful; and

FIG. 8 is a section taken substantially through 8-8 of FIG. 7 to moreclearly illustrate the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although specific examples willbe illustrated showing certain common types of applications of flexiblemembers, it is to be understood that the concept disclosed in thisinvention is equally applicable to flexible members of all sizes andshapes. These particular features will depend upon the apparatus inwhich the members are used. It should also be noted that althoughparticular reference is made to pneumatic systems, the principledisclosed in this invention will apply equally to other fluid systemswhich use various liquids or gases such as oil or nitrogen.

For the purposes of illustration, FIG. 1 shows a flexible member 1which, in this example, is of the type used in vehicle shock absorbersystems referred to as a sleeve type rolling lobe air spring. Asillustrated, this flexible member 1 is tubular with an essentiallyelongated cylindrical shape having an inside diameter of approximately 111/16 inches and a wall thickness of 0.110, plus or minus 0.010 inch andis generally about 1 foot in length. Preferably, it is formed of rubberor other elastomeric material with a fabric reinforcement containedtherein.

FIG. 2, a section taken through 2-2 of FIG. I, illustrates the cordfabric reinforcement 2, usually nylon, and the normal flex wrinklepattern 3 reproduced on the inner surface 4 of flexible member 1. Thepattern 3 has been reproduced from the actual flex wrinkle pattern of aflexible member which has been subjected to normal operating conditionsin a vehicle suspension system or facsimile thereof (such as a flex testunit) for a sufficient period of time to create the wrinkle pattern. Dueto the particular operating characteristics of the rolling lobe airspring, the actual flex wrinkle pattern is formed on the inner orcompression surface of the rolling torus of the flexible member. In thisway, the actual flex wrinkle pattern is simulated on the inner surface 4of the flexible member 1 with the wrinkles 5 acting as hinge points tolocate and alleviate the stresses that will be created when flexiblemember 1 is operating in the system. The depth of the wrinkles 5 in theactual or simulated wrinkle pattern is generally in the range of 0.005to 0.018 inch but, of course, will vary depending upon the length oftime that the flexible member has been operating. Obviously, it isessential to reproduce the pattern 3 in at least the area of theflexible member 1 which is subjected to the maximum flexing. Thelocation and extent of the area will depend upon the particularapplication and consequently must be determined for each application.

Various methods may be used to reproduce the actual flex wrinkle patternthereby forming the predetermined flex wrinkle pattern on the surface ofthe flexible member. One method successfully employed is as follows:

1. Make a longitudinal cut in the flexible member of the rolling lobeair spring after it has operated for a sufficient period to create aflex wrinkle pattern.

2. Cut out the portion of the flexible member which has been subjectedto the maximum flexing and therefore contains the actual flex wrinklepattern.

3. Mount this portion on a substantially flat base by means of anadhesive.

4. Enclose the periphery of the mounted portion to form a mold.

5. Form a pattern of an opposite configuration or contour from that ofthe actual flex wrinkle pattern by pouring a substance such aspolyurethane into this mold.

6. Attach the polyurethane pattern to a mandrel or molding core so as tobe substantially flush with the surface. Preferably, the pattern isadhered to the mandrel by means of an adhesive vulcanized under heat andpressure.

7. Place a sleeve of unvulcanized elastomeric material over the mandrelthen vulcanize under heat and pressure to produce the simulated flexwrinkle pattern on the inner surface of the flexible member.

The foregoing method, although effective, has the disadvantage of beingtime consuming and too costly when a large number of patterned mandrelsmust be produced to meet the production requirements of the flexiblesleeves. Therefore, a compromise procedure has been developed in whichthe flex wrinkle pattern is approximated by determining the common orpredominate distance or pitch of adjacent wrinkles of the actual flexwrinkle pattern then producing a plurality of grooves or corrugations atthis spacing on the inner surface of the flexible member. The groovesare formed preferably in the surface of the flexible member duringmolding under heat and pressure but other methods may also be used, suchas machining the grooves on the already vulcanized product. As aminimum, these grooves are placed in the portion of the flexible memberwhich will be subjected to the maximum flexing during its operation inthe fluid pressure system, but for convenience, they may be formed inother areas as well without affecting the operation of the flexiblemember. I Although any type of corrugated or convoluted contour will actto relieve the stresses in the flexible member, it is important thatalternate flat or land portions of greater width than the grooves beprovided between the grooves. This will prevent objectionable noisetransfer and the possible interleaving of the corrugations during therolling motion of the flexible member.

In the just described procedure, the grooves act as the hinge points tolocate and alleviate the stresses created during the operating of theflexible member thus serving in much the same manner as the wrinkles ofthe flex wrinkle pattern. In addition, since the grooves are uniformlyspaced, this structure has the advantage of uniformly located stressareas to provide for a uniform distribution of the stresses when theflex member in operating. It has been determined that the best generaldurability is obtained with a groove depth of 0.010 to 0.018 inch. Incold weather, in addition to the advantage of the hinge points providedby the corrugations, the reduced wall gauge at the grooves also impartsmore flexibility to the flexible members. Furthermore, the grooves actto facilitate the operation of the flexible member by reducing theresistance to the rolling motion particularly at low pressures. Thesegrooves may take various forms as will become apparent.

One form of the invention shown in FIG. 3 illustrates a flexible memberproduced by using the compromise procedure. The flexible member 1 isagain of the type used in a rolling lobe air spring and hascircumferential grooves 6 and alternate flat or land portions 7uniformly positioned longitudinally along substantially the entirelength of the flexible member 1. The pitch 8 of the grooves 6 issubstantially equal to pitch 9 of the wrinkles 5 shown in FIG. 2. Intheory, the wrinkle pitch 9 is generally determined by suchcharacteristics as the size, shape wall thickness, inflation diameter,and roll radius of the flexible member as well as by the design of theparticular piston assembly. For example, it has been determined that aflexible sleeve of a rolling lobe air spring with an inside diameter of1 11/16 inches after operating for a period of one million cycles in aflex test unit has a wrinkle pitch of approximately 43 inch. Also it hasbeen determined that this type flexible sleeve when removed from avehicle shock absorbing system after 25,000 miles of normal usagedeveloped essentially this same pitch. Accordingly, the pitch 8 of thegrooves 6 should also be /8 inch. As previously mentioned, grooves 6take the place of the wrinkles 5 of the predetermined flex wrinklepattern 3 to control the flexing and alleviate the stresses in theflexible member I. As shown, a series of longitudinal ribs 10 are formedon the surface of the flexible member, from a series of correspondinglongitudinal grooves in the mold, the purpose of which will be explainedlater.

One method of forming these circumferential grooves is shown in FIG. 4.As illustrated, a steel mandrel or molding core 11 has a plurality ofcircumferential ridges or peaks 12 on the outer surface and uniformlyspaced along the length thereof with alternating flat or land portions13 of greater width than the ridge l2 therebetween. Preferably,longitudinally extending grooves 14 on the surface of mandrel 11 serveas venting means to permit, during the molding operation, the escape oftrapped air. The flexible member 1 is positioned over the mandrel l1 andvulcanized under heat and pressure thus forming grooves 6 and flatportions 7, as well as ribs 10 on the inner surface 4 of the flexiblemember 1. FIG. 5 is a modification of the invention shown in FIG. 3 inwhich the flexible member 1 contains a plurality of helical grooves 6Amolded on its inner surface 4.

Another modification of the invention shown in FIG. 3 is illustrated inFIG. 6 in which flexible member 1A is tapered gradually in thelongitudinal direction. The purpose of the tapered design is to furtherfacilitate the functioning of the flexible sleeve rolling lobe airspring member which tends to take on a longitudinally taperedconfiguration after extended periods of operation. Of course, thegrooves 6 may also be either circumferential or helical in this design.It is also important to recognize that in addition to the rolling lobetype air spring, the teaching of this invention may be applied to allpiston type air springs with little or no modification required.

Another type of flexible member of the same general classification asthat used in the rolling lobe air spring is the rolling sleeve diaphragmshown in FIG. 7 which is used in air brake control systems. Flexiblemember 1B is normally of a cup or hat-shaped configuration with closedbase 15 and a cylindrical sidewall 16. It is generally composed ofelastomeric material such as rubber or the like and reinforced by atextile cord or square woven fabric such as cotton or nylon. However, itmay also contain no reinforcement and be formed of a material such aspolyurethane. The maximum flexing in this member takes place on theinner or compression surface 17 of the rolling torus which is inproximity to the peripheral edge portion or lip 18 at the open end 19 ofthe flexible member 18. The predetermined flex wrinkle pattern may beimparted to this area of the flexible member 18 by means of a mold (notshown) having a molding surface of opposite configuration from that ofthe actual flex wrinkle pattern. Here again, however, it is much morepractical and economical to use a molding surface, as previouslydescribed, containing a plurality of ridges or peaks positioned in thearea of maximum flexing and having the required pitch between the ridgesto form the product as shown in FIG. 8.

FIG. 8 is a section takenthrough 8-8 of FIG. 7 showing the fabricreinforcement 20 and a plurality of essentially circular grooves 21substantially adjacent to the peripheral edge portion 18 on the innersurface 17 at the open end 19 of flexible member 13. These grooves 21,of course, function in the manner mentioned previously. Althoughparticular reference has been made to the rolling sleeve diaphragm, itshould be apparent to those skilled in the art that the invention isequally applicable to other forms of flexible diaphragms such as thelong stroke, convoluted, or

dished type.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

l. A method of increasing the service life of flexible resilient membersof the type used in a fluid pressure system in which a first flexibleresilient member undergoes a rolling motion which creates a flex wrinklepattern on a surface of said first member after a period of flexingduring the operation of such system, said method comprising the step ofintentionally producing a simulation of said flex wrinkle pattern on asurface of a second flexible resilient member prior to its installationin a fluid pressure system by providing a plurality of grooves thereinat least in the area of the surface of said second member which will besubjected to the maximum flexing during the movement of said secondmember, said grooves positioned to substantially sim ulate andcorrespond to said flex wrinkle pattern.

2. The method as claimed in claim 1 wherein the distance between thecenterline of each adjacent groove is substantially equal to thedistance between the centerline of each adjacent wrinkle of said flexwrinkle pattern with the grooves being uniformly spaced on the surfaceof the member.

3. The method as claimed in claim 2 wherein the member is a tubularfabric-reinforced of fabric elastomeric material containing a pluralityof circumferential grooves uniformly positioned on the inner surfacethereof.

4. The method as claimed in claim 2 wherein the member is an essentiallyhat-shaped member of fabricreinforced elastomeric material containing aplurality of circular grooves uniformly positioned on the inner surfaceand adjacent the peripheral edge of the open end thereof.

5. The method as claimed in claim 2 wherein the producing step comprisesfirst vulcanizing said second flexible member and then machining saidgrooves into the surface of said second flexible member.

6. A method of producing flexible resilient pressureretaining membersfor use in fluid pressure systems of the kind in which at least one ofthe peripheral edge portions of such a flexible member is attached tothe body structure of such system to create a fluid-tight chamber, saidbody structure containing elements movable in an axial directionrelative to each other with the movement causing a rolling motion in theflexible member, said method comprising the steps of determining theactual flex wrinkle pattern created on the surface of a flexible memberwhich has been subjected to a period of flexing in the operation of suchsystem, and intentionally producing on the surface of subsequentflexible members, prior to their installation in such fluid pressuresystems, in at least the area of said subsequent flexible members whichwill be subjected to maximum flexing in service in such system a patternof grooves in at least substantially the same pattern as said actualflex wrinkle pattern to thereby control the flexing and distribution ofstresses in said subsequent flexible members.

7. The method as claimed in claim 6 wherein the pat tern-producing stepincludes preparing from the actual flex wrinkles a mold to reproduce theflex wrinkle pattern on the surface of subsequent flexible members, andmolding said subsequent flexible members in said mold whereby the flexwrinkle pattern is formed in at least the area of maximum flexing of theflexible members.

8. The method as claimed in claim 6 wherein the method includesapproximating the flex wrinkle pattern by determining the predominatedistance between the centerline of each adjacent wrinkle of the actualflex wrinkle pattern created on the surface of a flexible member after aperiod of flexing during the operation of such system, forming aplurality of ridges on a molding surface with the distance between thecenterline of each adjacent ridge being substantially equal to thedistance between the centerline of each said adjacent wrinkle of theflex wrinkle pattern, and molding a flexible member against said moldingsurface to conform the flexible member to the molding surface therebyforming a plurality of grooves on the surface thereof to provide hingepoints to control the flexing of the flexible member.

9. The method as claimed in claim 6 wherein the member is a tubularsleeve of fabric-reinforced elastomeric material containing a pluralityof circumferential grooves uniformly positioned on the inner surfacethereof.

10. The method as claimed in claim 6 wherein the member is anessentially hat-shaped member of fabricreinforced elastomeric materialcontaining a plurality of circular grooves uniformly positioned on theinner surface and adjacent the peripheral edge of the open end thereof.

11. The method as claimed in claim 6 wherein the distance between thecenterline of each adjacent groove is substantially equal to thedistance between the centerline of each adjacent wrinkle of the actualflex wrinkle pattern with the grooves being uniformly spaced on thesurface of the member.

12. The method as claimed in claim 11 wherein the producing stepcomprises first vulcanizing said subsequent flexible members and thenmachining said grooves into the surface of said subsequent flexiblemembers.

1. A method of increasing the service life of flexible resilient membersof the type used in a fluid pressure system in which a first flexibleresilient member undergoes a rolling motion which creates a flex wrinklepattern on a surface of said first member after a period of flexingduring the operation of such system, said method comprising the step ofintentionally producing a simulation of said flex wrinkle pattern on asurface of a secOnd flexible resilient member prior to its installationin a fluid pressure system by providing a plurality of grooves thereinat least in the area of the surface of said second member which will besubjected to the maximum flexing during the movement of said secondmember, said grooves positioned to substantially simulate and correspondto said flex wrinkle pattern.
 2. The method as claimed in claim 1wherein the distance between the centerline of each adjacent groove issubstantially equal to the distance between the centerline of eachadjacent wrinkle of said flex wrinkle pattern with the grooves beinguniformly spaced on the surface of the member.
 3. The method as claimedin claim 2 wherein the member is a tubular fabric-reinforced of fabricelastomeric material containing a plurality of circumferential groovesuniformly positioned on the inner surface thereof.
 4. The method asclaimed in claim 2 wherein the member is an essentially hat-shapedmember of fabric-reinforced elastomeric material containing a pluralityof circular grooves uniformly positioned on the inner surface andadjacent the peripheral edge of the open end thereof.
 5. The method asclaimed in claim 2 wherein the producing step comprises firstvulcanizing said second flexible member and then machining said groovesinto the surface of said second flexible member.
 6. A method ofproducing flexible resilient pressure-retaining members for use in fluidpressure systems of the kind in which at least one of the peripheraledge portions of such a flexible member is attached to the bodystructure of such system to create a fluid-tight chamber, said bodystructure containing elements movable in an axial direction relative toeach other with the movement causing a rolling motion in the flexiblemember, said method comprising the steps of determining the actual flexwrinkle pattern created on the surface of a flexible member which hasbeen subjected to a period of flexing in the operation of such system,and intentionally producing on the surface of subsequent flexiblemembers, prior to their installation in such fluid pressure systems, inat least the area of said subsequent flexible members which will besubjected to maximum flexing in service in such system a pattern ofgrooves in at least substantially the same pattern as said actual flexwrinkle pattern to thereby control the flexing and distribution ofstresses in said subsequent flexible members.
 7. The method as claimedin claim 6 wherein the pattern-producing step includes preparing fromthe actual flex wrinkles a mold to reproduce the flex wrinkle pattern onthe surface of subsequent flexible members, and molding said subsequentflexible members in said mold whereby the flex wrinkle pattern is formedin at least the area of maximum flexing of the flexible members.
 8. Themethod as claimed in claim 6 wherein the method includes approximatingthe flex wrinkle pattern by determining the predominate distance betweenthe centerline of each adjacent wrinkle of the actual flex wrinklepattern created on the surface of a flexible member after a period offlexing during the operation of such system, forming a plurality ofridges on a molding surface with the distance between the centerline ofeach adjacent ridge being substantially equal to the distance betweenthe centerline of each said adjacent wrinkle of the flex wrinklepattern, and molding a flexible member against said molding surface toconform the flexible member to the molding surface thereby forming aplurality of grooves on the surface thereof to provide hinge points tocontrol the flexing of the flexible member.
 9. The method as claimed inclaim 6 wherein the member is a tubular sleeve of fabric-reinforcedelastomeric material containing a plurality of circumferential groovesuniformly positioned on the inner surface thereof.
 10. The method asclaimed in claim 6 wherein the member is an essentially hat-shapedmember of fabric-reinforced elastomeric material containing a pluralityof circular grooVes uniformly positioned on the inner surface andadjacent the peripheral edge of the open end thereof.
 11. The method asclaimed in claim 6 wherein the distance between the centerline of eachadjacent groove is substantially equal to the distance between thecenterline of each adjacent wrinkle of the actual flex wrinkle patternwith the grooves being uniformly spaced on the surface of the member.12. The method as claimed in claim 11 wherein the producing stepcomprises first vulcanizing said subsequent flexible members and thenmachining said grooves into the surface of said subsequent flexiblemembers.